Greenhouses are used especially in middle latitudes and provide a more consistent and warmer climate than outdoor cultivation. Therefore, greenhouses are heated, if required or modern greenhouses are air-conditioned in the summer, which results in high power consumption. Previous improvements of the energetic efficiency of greenhouses have resulted especially in more cost-effective energy production or an improvement of the heating system. However, by improving heat insulation a better saving potential can be achieved.
It is known to use double-skin sheets and multi-layer cross-braced plates consisting of transparent plastic material, as well as double glazed windows to improve the insulation of transparent buildings, such as greenhouses. Furthermore, underneath foils or special screen installations to save energy are put into greenhouses, for example (AT 503 879 A1).
Double-skin sheets have the disadvantage that during a period of between 8 and 22 years they loose transparency and stability. When insuring a building covered with transparent plastic material, the refund amount of the insurance companies decreases during the product lifetime in a period of between 8 and 22 years, depending on the material. Thus the refund amount decreases from 100% to 0%.
Because of the heavy weight, double glazed windows have the disadvantage that the greenhouses require a stronger construction. Double glazed windows are rarely used for greenhouses because the material, as well as the reinforcement of the structure are very expensive.
Energy shields have the disadvantage of an expensive installation, even with a respective provision for opening and closing. The durability lies between 6 and 10 years. Underneath foils last only 2 to 5 years.
In AT 503 879 A1, the suggestion is made to insert an air cushion between two energy shields or two sheets of foil. Insurance companies calculate the durability of such materials at up to 8 years. It is therefore debatable how the insulation effect has been reduced already after 4 years. What is more, up to the energy shield the pediment region of the greenhouse is not insulated, requiring an increased heat output at the start of the day when the energy shield is opened.
Also known is vacuum insulated glass (VIG). Here individual columns are arranged between two glass panes. Even in this case the high weight and expenses are disadvantageous. In addition, it is difficult to produce a vacuum-tight connection between two float glass panes.